NASA to try 5th launch attempt today

MIKE SCHNEIDERAssociated Press Writer

Published Saturday, September 09, 2006

CAPE CANAVERAL -- For the fourth time in two weeks, NASA nixed the launch of the space shuttle Atlantis, this time for a faulty fuel tank sensor -- the same glitch that has thwarted two other missions.

A fifth liftoff attempt will be made at 11:15 a.m. EDT Saturday to get the spacecraft headed on a mission to resume construction of the international space station.

On Friday the six astronauts were already strapped in with the hatch closed when the space agency called off the launch with just 45 minutes to go. Although the fuel sensor had malfunctioned hours earlier, NASA wanted to keep discussing the problem before scrubbing the flight.

But they knew the odds for a liftoff weren't good. The agency has a new rule requiring a stand-down of 24 hours when one of the hydrogen tank's four engine cutoff sensors doesn't work properly; such a delay would allow engineers to gather more data on the problem.

"We had a lot of discussion. ... We follow the rules," launch director Mike Leinbach radioed Atlantis' crew, notifying them about the scrub. "Ought to feel good that we did that."

"We understand. We concur 100 percent," responded Atlantis' commander, Brent Jett. "It was given a lot of thought by a lot of smart people ... It's the right thing to do."

A large number of managers favored flying, but opposition to launching was led by NASA's flight crew operations director.

"... When you get into the launch countdown, there are emotions running a little bit higher," said shuttle program manager Wayne Hale. "But at the end of the day, we decided staying with the plan ... was the prudent thing to do."

The new plan for the 24-hour delay was implemented after two previous encounters with faulty fuel tank sensors. Earlier this year, Discovery's launch was delayed by almost two months so four tank sensors could be replaced after one was found to be faulty, and a similar problem briefly delayed last summer's launch of Discovery on the first shuttle flight since the Columbia disaster in 2003.

The fuel gauges are designed to prevent the main engines from running too long or not long enough during the climb to space. An engine shutdown at the wrong time could prove catastrophic, forcing the astronauts to attempt a risky emergency landing overseas, or leading to a ruptured engine. NASA managers are confident the shuttle can launch successfully with only three of the four sensors working properly.

"If everything is performing as expected and we just have one sensor that continues to be a bad actor, we'll launch tomorrow," Hale said Friday.